1. Field of the Invention
The present invention relates to the technical field of image processing and, more particularly, to a color reconstruction system and method for a Sequential Color with Memory (SECAM) television signal.
2. Description of Related Art
FIG. 1 is a schematic diagram of a typical Sequential Color with Memory (SECAM) signal coding. As shown in FIG. 1, the SECAM signal coding uses two chrominance signals DB and DR to represent the color signals. The signals are presented on the scan lines in interlacing. Namely, the chrominance signals DB and DR on the scan lines are sequentially interlaced. A chrominance signal DB of the SECAM signal is generated by subtracting the luminance signal Y from the blue signal B of an RGB signal. Similarly, a chrominance signal DR of the SECAM signal is generated by subtracting the luminance signal Y from the red signal R of the RGB signal. At the transmitting end, the chrominance signals DB and DR of the SECAM signal are modulated by different frequency subcarriers for output.
As shown in FIG. 1, the chrominance signal DB is present on Line 110 only, and the chrominance signal DR is present on Line 120 only. Accordingly, the decoder at the receiving end typically requires one scan line delay, and the output signal after decoding can have both the chrominance signals DB and DR through an interpolation operation. FIG. 2 is a block diagram of a typical SECAM signal decoder. When a SECAM signal is received, the luminance and chrominance separator 210 can separate the luminance signal Y from the chrominance signal (DB, DR). Subsequently, the color demodulator 220 performs a frequency demodulation on the chrominance components. Since each scan line of the SECAM signal contains only a chrominance signal DB or DR, the demodulation performed by the color demodulator 220 is taken by detecting the subcarrier frequencies to thereby identify the chrominance signal DB or DR contained by each scan line and produce a DB/DR identification signal. Thus, the DB signal output by the color demodulator 220 can be determined as the currently or previously received scan line, and the DR signal is also the same. Accordingly, it can be known that the DB or DR signal is to be reconstructed.
FIG. 3 is a schematic diagram of a typical DB/DR signal reconstruction. Line 120 at Time T only contains the DR signal, so that the DB signal reconstruction is necessarily taken for Line 120. As shown in FIG. 3, the conventional process regards the DB signal in the previous line (Line 110) as the DB signal of Line 120 at the corresponding position. The DB signal in the previous line is stored in the line buffer block 230. Thus, the problem that only the chrominance signal DR is contained in Line 120 is overcome. In FIG. 3, the circle sign indicates the transmitting DB and DR chrominance signals, and the hexagonal sign indicates the reconstructed DB and DR chrominance signals.
However, the scan lines respectively in two adjacent frames at same positions contain the interlaced chrominance signals DB and DR. Namely, for example, Line 120 in Frame T only contains the DR signal, and Line 120 in Frame T+1 only contains the DB signal. Accordingly, for the boundaries in the vertical direction, the tandem frames may appear the unmatched DB and DR signals on the lower boundaries to thus cause the flicker effect. For example, when Line 120 indicates an object boundary in a frame, the colors of the object (Line 120) and the background (Line 130) are significantly different, and the chrominance signals DB of Pixel 121 and Pixel 131 are significantly different. However, the chrominance signal DB for Pixel 131′ in the prior art is derived from Pixel 121 as a copy, which causes a color dispersion at the boundary between Line 120 and Line 130 in Frame T+1 and have the different chrominance signals DB for Pixel 131 and Pixel 131′. Thus, the frame flicker is present.
U.S. Pat. No. 5,844,617 has disclosed a method and apparatus for enhancing the vertical resolution of a television signal having degraded vertical chrominance transitions, which converts a 4:2:0 format signal back to a 4:2:2 format signal by enhancing the vertical color resolution, i.e., enhancing the vertical bandwidth, to thereby use the high frequency information to determine the level of adding the high frequency color components back to the original color signal. However, the SECAM encoder typically bypasses the vertical low pass filter (LPF) and simply sends the current DB or DR signal. Contrary to the U.S. Pat. No. 5,844,617, the decoder does not require the high frequency component restored in the SECAM decoding. In addition, the signal received by the SECAM is not the 4:2:0 format.
Therefore, it is desirable to provide an improved method to mitigate and/or obviate the aforementioned problems.